The 3.0 software (which still appears not to have a hold mode) works on the first-generation Nest, too, so the only major improvements seem to be a slimmer design and compatibility with more complex systems:

The new Nest is 20% thinner than the original and encased by a premium solid stainless steel ring that clearly reflects the wall colors around it. Even Nest’s display is more streamlined - the sensor grille on the bottom of the original Nest has been replaced by a smooth lens.

I’m also curious to hear about how that “smooth lens” works in practice. How is the room temperature measured? Assuming it’s not somehow measuring it through that lens, is it measuring it through the back? I have a proprietary air-conditioner thermostat that measures through the back, and it’s awful, always misreading the room temperature by 2–5°F in either direction and swinging the room’s temperature wildly. Hopefully, the new Nest doesn’t have that problem.

It doesn’t appear that Nest has done anything about the effective C-wire requirement for heat-only systems, although they can’t, really. They have changed the base design for “easier installation”, but it was pretty easy before. The hardest parts are mounting it cleanly and securely in the drywall and getting the wiring working properly, neither of which can realistically be made much easier.

So this looks like a nice improvement for new buyers, but (fortunately for me) not a reason to upgrade for first-generation Nest owners.